Back in high school (a long time ago, but bear with me), my mother and I had an argument about Neil Young. I'd been blaring one of his albums — "Rust Never Sleeps"? "Zuma"? — and she came to my room to tell me to turn it down. When I protested that Young was a genius, my mother looked at me as if I were speaking a language she didn't understand.

"If he was a genius," she told me, "he wouldn't be playing electric guitar."

I kept thinking about that conversation as I made my way through Young's "Waging Heavy Peace: A Hippie Dream," which is surely one of the most idiosyncratic rock star autobiographies I've encountered, a book that wears its genius (yes) and its excess on its sleeve. A 500-page free-form series of digressions, it is by turns exhilarating and enervating, less a memoir than a self-portrait, with all the impressionism that implies.

On the one hand, "Waging Heavy Peace" is a mess — sprawling, improvisational, like a sloppy 40-minute jam on "Like a Hurricane." But it is also revealing, even (at times) oddly beautiful, a stream-of-consciousness-meditation on where Young has been, where he thinks he's going and, perhaps most revealing, where he is right now.

"Not that it matters much," he tells us, "but recently I stopped smoking and drinking.... The big question for me at this point is whether I will be able to write songs this way. I haven't yet, and that is a big part of my life. Of course I am now sixty-five, so my writing may not be as easy-flowing as it once was, but on the other hand, I am writing this book. I'll check in with you on that later. We'll see how it goes."

The smoking to which Young refers is, of course, weed, which he has long regarded as a key to his creativity. As such, his not altogether willing sobriety becomes one of the threads of "Waging Heavy Peace," a through line that roots the book in the here and now. Composed in 2011, during a period when Young had stopped making music, the memoir is as much a record of his creative doubts, his fears and uncertainties about growing older, as it is the story of his years with Buffalo Springfield or Crosby, Stills, Nash and Young.

"At this age," he writes, contemplating another run with Crazy Horse, his longtime backing band, "I think relevancy is the big challenge.... We need to be sure the new songs and music are ready and are meaningful to us. They are our ticket, our vehicle to the future, and without the new songs we are just reliving the past."

As it turns out, the Crazy Horse reunion did happen; Young and the band released a cover record this year, and an album of new songs, "Psychedelic Pill," comes out at the end of the month. (They play the Hollywood Bowl on Oct. 17.) But it is compelling to see a figure as prominent as Young — arguably one of the five or 10 most influential figures in the history of rock 'n' roll — express himself in such an unfiltered way.

"As you can tell," he writes, in one of many direct asides to his readers, "if you are still with me, I don't have much control over that. I have only rewritten about one paragraph so far. There is no such thing as a spell-check for life, though. There is a big wind blowing today, and I'm part of it. I want to make a difference, and above all, I want to be a good person from here on out."

This off-handed directness has long been the key to Young's music; he's as unpretentious as they come. Even "Trans," his 1982 electronic album, had its roots in day-to-day experience, inspired by his son Ben, who was born with cerebral palsy and requires around-the-clock care.

And yet, Young is mercurial and easily distracted, as evidenced by the peripatetic nature of his career. He followed his most commercial record, 1972's "Harvest," with a suite of albums ("Time Fades Away," "On the Beach," "Tonight's the Night") known among his fans as the "Ditch Trilogy," for their distance from the middle of the road. He walked away from every group he ever played with, famously breaking up with Stephen Stills midtour in 1976 by sending Stills a telegram that read, "Funny how some things that start spontaneously end that way. Eat a peach, Neil."

Tellingly, that anecdote doesn't appear in "Waging Heavy Peace." There's a limit to the art of revelation, I suppose. But it remains instructive, suggesting something about Young's approach to this project as well. Like his discography, it is a memoir without apparent shape — or more accurately, one whose shape emerges from its shapelessness, from its tendency to wander, from the ebb and flow of Young's attention, from the play of memory. In many ways, it unfolds in real time, with ruminations on his sobriety, on extra-musical projects such as the Lincvolt (an electric car) or PureTone (a system for reproducing digital sound in high fidelity) as well as ongoing updates on the book itself.

"I have been clean now for seven months," he writes in one of the closing chapters. "That is a good long time. I still feel cravings. Maybe I'd like a beer, maybe a joint.... I haven't written a song in more than half a year, and that is different for me. Of course I've written over ninety thousand words in this book, and that is different for me, too."

What you make of it has a lot to do with what you make of Young: not the Young of "Harvest" or "After the Gold Rush" but the creator of the "Ditch Trilogy." Like those records, "Waging Heavy Peace" is not a work for the casual fan or the crossover reader in the vein of, say, Keith Richards' "Life" or Patti Smith's "Just Kids."

Still, this gives the book an authenticity that has less to do with the stories Young tells than with how he tells them, his tendency to look not backward but ahead.

"Why so pensive about the past?" he asks. "What can it say or do for you now?" Strange questions for a rock star autobiography but at the same time a reminder of what sets Young apart.

"How am I," he goes on, "some forty years down the road, to deal with that past accomplishment? Cast it off? Relinquish it to the others who value it more? Was it me? Or who am I now that I cannot see or meet myself the way I was? That is not for me to know, because I am busy with new things now and have no time at all."